Azathioprine is an immunosuppressive drug used to treat various immune-mediated or autoimmune diseases in dogs. Generally, it is not used as a sole therapy, but is administered in addition to other immunosuppressive drugs. Given the seriousness of some of the adverse reactions associated with its administration, it is important to carry out periodic controls during treatment and withdraw the drug whenever serious adverse effects are detected.
What is azathioprine?
Azathioprine is a potent immunosuppressive drug used to treat immune-mediated or autoimmune diseases. It is a synthetic analog of purine, which exerts its immunosuppressive effect by inhibiting DNA synthesis at the level of B and T lymphocytes. In this way, manages to interrupt the division of cells of the immune system and, thereby, modulates the immune response.
Currently, in Spain no veterinary medicinal product containing azathioprine is marketed for use in dogs. For this reason, when your veterinarian decides to start a treatment with azathioprine, they should resort to the so-called “cascade prescription”, which consists of prescribing a drug that is not authorized for a specific animal species when there is a therapeutic gap. Oral formulations (tablets) are generally prescribed and are marketed for use in people.
What is azathioprine used for in dogs?
Azathioprine is used to treat immune-mediated or autoimmune diseases, which are those in which the immune system attacks or destroys components of the body by recognizing them as foreign.
Generally, a clinical response is not seen for 4-8 weeks. Therefore, azathioprine is usually administered in addition to other immunosuppressive drugs (generally corticosteroids) that constitute the mainstay of treatment. In this way, it is possible to reduce the dose of the main drugs and, with it, the adverse effects associated with high doses and their prolonged use.
Azathioprine uses in dogs
As we have explained, azathioprine in dogs is used as an immunosuppressive drug in the treatment of immune-mediated or autoimmune diseases. Specifically, it is usually prescribed for the treatment of the following immune-mediated pathologies in dogs:
- Immune-mediated hemolytic anemia
- Immune-mediated thrombocytopenia
- Inflammatory Bowel Disease or IBD
- Immune-mediated hepatitis
- Immune-mediated meningoencephalitis
- Rheumatoid arthritis
- Lupus erythematosus
- Pemphigus foliaceus
- Myasthenia gravis
Dose of azathioprine in dogs
The dose of azathioprine in dogs tends to vary throughout treatment. Specifically, the therapeutic protocol for azathioprine in dogs is usually as follows:
- Initially, an induction dose of 1.5-2.5 mg per kg body weight per 24 hours.
- Once the lesions subside or the symptoms are controlled, it can be administered every other day.
- In the long term, the dose can be reduced to 0.5-2 mg per kg of body weight every 72 hours.
Azathioprine side effects in dogs
Azathioprine is an immunosuppressive drug that is frequently used to treat immune-mediated diseases in dogs, however, its use is not exempt from the appearance of adverse reactions.
Below, we collect the main side effects of azathioprine in dogs:
- Medullary aplasia (myelotoxicity): disappearance of the bone marrow tissue responsible for producing blood cells (red blood cells, white blood cells and platelets). As a consequence, anemia (decreased red blood cells), leukopenia (decreased white blood cells) or thrombocytopenia (decreased platelets) may appear.
- Digestive signs: diarrhea, vomiting and anorexia.
- Greater susceptibility to infections: its immunosuppressive effect makes the body more unprotected against pathogens, thus increasing the incidence of secondary infections
- Liver toxicity (hepatotoxicity): with increased ALT (alanine aminotransferase) enzyme
- Pancreatitis: with increased pancreatic amylase and lipase
- Skin reactions.
Given the myelotoxic and hepatotoxic potential of azathioprine, it is recommended to carry out periodic hematological and biochemical controls At the start of treatment they should be carried out analysis every 2-4 weeks, and then every 3 months. Whenever an alteration is detected in routine controls, treatment should be withdrawn.
Azathioprine contraindications in dogs
There are certain situations in which the administration of this immunosuppressant may be counterproductive. Specifically, the contraindications for azathioprine are:
- Allergy to azathioprine, to mercaptopurine (a metabolite of azathioprine) or to any of the excipients contained in the drug.
- Severe infections.
- Serious liver function impairment.
- Serious bone marrow impairment.
- Pancreatitis.
- Pregnancy: since it is a teratogenic and embryotoxic compound.
- Breastfeeding: since it is excreted with milk.
- Vaccination: Vaccines should not be administered during treatment as the drug may interfere with the effectiveness of the vaccination.
In addition, it is important that you inform your veterinarian about any other treatment your dog may be receiving, in order to avoid the risks associated with certain drug interactions. Specifically, azathioprine may interact with:
- Xanthine oxidase inhibitors: such as allopurinol.
- Anticoagulants: such as warfarin.
- Other immunosuppressants: such as cyclosporine or tacrolimus.
- ACEIs (Angiotensin Converting Enzyme Inhibitors): such as enalapril or benazepril.
- Aminosalicylates: such as sulfasalazine.
